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Old 05-09-2020, 13:21   #1
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Rainwater harvesting

I'm planning my bimini design, which will be a rigid affair using two 300w solar panels and a lightweight composite sheet in the middle. I have been planning to make it double as a rainwater catching system, but the more I think about it, the more difficult this seems.

I've noticed that lots of cruisers just set up a tarp as a rain catcher. I'm starting to wonder if this is a much better idea. OK I might miss out on some rain catching opportunities, but the tarp will stay nice and clean, and it will save me a bit of head-scratching with my bimini design.

Which way would you guys go? How much of a pain is it to rig and de-rig a tarp every time you spot a cloud heading your way?
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Old 05-09-2020, 13:34   #2
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Re: Rainwater harvesting

a rain catching system really needs to be permernantly rigged to be effective.
problem with tarps is rain generally arrives with wind which lifts the tarp ,plus they get in the way whilst sailing.

a dodger system needs a good lip on it or some sort of gutter to catch the rain even when the boat is heeling.

also there needs to be at least 1 inch diameter hose led ideally to cans in the cockpit so any debris can be filtered out before putting into the tanks.
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Old 05-09-2020, 14:55   #3
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Re: Rainwater harvesting

In my experience most attempts to catch rain from biminis end in water everywhere except the tank. To say it works but takes plenty of design effort.

I found the following to work very well:

- underway - mainsail - a gutter at the foot tubed to a small tank,
- anchored - leave the dinghy in the water, collect water from the dinghy next morning,
- dedicated - a special tent 'reversed' with a water outlet in the center.

The tent, as atoll says, tends to be not easy to manage in a squall and most tropical rain comes in a squall, but we had 100% success by simply tying the center with a strop to the deck.

If you build a raincatcher tent, aim high - it needs quite some slope and then it needs to fit a big jerrycan bellow. Ours hangs maybe 5 ft above the deck and catches beyond 300 liters in a heavy Caribbean downpour. It is 2 meters wide and 3 meters long. It is attached to aft shrouds and to the frame that supports our boom. I used plain acrylic cloth, non-impregnated.

When it is sunny I simply let the deck strop go and tie it to a main halyard - now we have a deck tent (friends look at us, laugh and say we are running a circus!

Still, my fave method is the dinghy method.

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Old 05-09-2020, 15:28   #4
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Re: Rainwater harvesting

We had an awning that went from mast to boom gallows at the stern, midpoint lifted by the main halyard and two bamboo stretchers. Installed plastic through-hulls about midway on each side. Would pull them down to create a low point and cleat line to deck and run hose from them to the tank to collect water. Awning was always up at anchor so just had to attach hose and pull down the through-hull to collect water. Worked fine for a year in FP, never had to schlep water as the awning provided all we needed. For most places with regularly reasonable showers an awning should work if you're the least bit careful with your water consumption. Won't work in Baja or other places with infrequent rain.

A bimini could work the same way though it's area is a bit limited.

We never had a problem with running short of water on passages as long as 30 days so didn't set up a way to collect water under way. The round the world guys used a gutter on the main to collect water but don't know they set it up.
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Old 05-09-2020, 15:33   #5
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Re: Rainwater harvesting

Bird poo, bat poo, what you going to do.
Drink it?
This is the start of the best science allowed..thread ever.
Lot funnier than running a water maker in toilet harbor.
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Old 05-09-2020, 15:35   #6
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Re: Rainwater harvesting

If you can build the bimini panel with a mini gutter all around seems it would work great! But yeah, you'd have to wash it I suppose.
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Old 05-09-2020, 15:39   #7
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Re: Rainwater harvesting

If your water tanks are filled through deck fittings, why not just put a rag behind them and open them up when it rains? This is the system we use on our trawler and it works very well and is dead simple.

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Old 05-09-2020, 15:57   #8
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Re: Rainwater harvesting

When we started cruising I made up a tarp with a hose but now when there is a good rain I wait a while 20 30 minutes for the deck to clean then put weighted baggies to dam water right into my tank. True a bird could come by in the rain but the same is true for a tarp or sail although if it is stored below it would start cleaner. My water tank fill is on deck and easy to dam. Simple and been successful without issues for years. Doesn't work for passing showers.
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Old 05-09-2020, 16:44   #9
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pirate Re: Rainwater harvesting

What I did (and would do again) when crossing the Pacific was hang a bucket at the gooseneck and use the topping lift to create a 10 degree incline on the boom..
The rain is driven against the bellied sail and runs down and forwards to deposit the bulk of the water in a stream into the bucket.
I experimented with tarps and other things first but these were pretty useless however after failing to get potable water at Nuku Hiva things were a bit serious for the onward trip to Samoa.. saw the water running by the gooseneck so gave it a go and it worked well.
I was using two buckets and switching as each filled.. about 5mins, however a bucket with a permanent hose fixed to the bottom long enough to reach a filler would save a lot of tooing and froing..

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Old 05-09-2020, 18:11   #10
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Re: Rainwater harvesting

I made a triangular catcher out of a plastic tarp that ties to the furled headsail (only used it when not sailing) and the shrouds. A typical garden hose fitting in the apex connected it to the fillers via a custom fitting I made.

We used it once or twice then I installed a watermaker. Where we cruise, rain is rare and not a dependable water source. Now I have a plastic tarp thingy that clogs a locker and needs to be thrown out.
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Old 05-09-2020, 18:56   #11
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Re: Rainwater harvesting

We used a cockpit awning that could also be used as a rain catcher. Jim designed it to have shape, and it was a trapezoid, made from 4 triangles. We sewed it from Sunbrella. Forward, it tied to the shrouds, aft to the backstay; it had a spreader astern. It had a loop for an uphaul (the main halyard), and a skin fitting with a barbed end on it for the hose. Did let it rain on it for a bit. Collected into 5 gal. clear collapsible jugs. Didn't use it for drinking if we could see particles, instead used it for washing clothes. Never hurt us. Did treat it (1 Tbsp. : 5 gal) with bleach, and filtered out the chlorine with a charcoal water filter, for drinking. It also keeps stuff from growing in your hoses.

Some Canadian friends of ours used a foredeck awning to a bucket, but the filler hose came out the side of the bucket--the bottom of the bucket caught particulates--and ran to the deck fills.

Some other Canadian friends washed the deck when the rain started, then used terry towels to make dams at the fills, and another couple, jammed hose through their perforated toe rails and hung buckets to catch the runoff, again with towel dams. One's whole boat, pretty much, being the catchment.

So there are many ways to solve the question.

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Old 05-09-2020, 19:00   #12
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Re: Rainwater harvesting

Building on what Ann mentioned; what if a valve installed on each scupper tube could be switched to divert deck water into a tank? My Alberg 30 has some scuppers on deck outside the cockpit coaming, so for me damming the fills as Ann mentioned would get deck water into the scupper drains. If you dont have drains on deck you could easily install some.. it'd be a bit more secure than buckets I suppose. Plus you would need to only open the pair of newly installed valves and probably close the thru-hull valves for safety. Probably do that last bit first, eh.
This seems like a great way to catch a lot of water that I'd personally filter and/or treat if drinking.
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Old 05-09-2020, 19:45   #13
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Re: Rainwater harvesting

We use the deck as a water collection system. The toerail is mostly closed and is about 4" high above the deck. All we need to do to collect rain is to push a towel in a couple of scupper holes, open the deck fill and with decent rain we have 100 gallon collected in as little as 20 minutes. We usually need to let it rain for about half an hour before we open the tank fill so that the salt and other contaminants wash off the deck.
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Old 05-09-2020, 19:51   #14
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Re: Rainwater harvesting

Originally Posted by Manateeman View Post
Bird poo, bat poo, what you going to do.
Drink it?
This is the start of the best science allowed..thread ever.
You are aware that tap water in the average city in the average country is a lot more dangerous to human health? Any idea of how much medication, antibiotics and hormones are in tap water, not to speak of arsenic and heavy metals? Especially the USA is going to get very bad very quickly now that the clean water act has been abolished by the current Whitehouse occupant.
We operate our "Bagheera" in the high Arctic for scientific, skiing, mountaineering, diving, research and adventurous expeditions.
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Old 05-09-2020, 20:00   #15
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Re: Rainwater harvesting

We became friends with live aboard locals in Martinique. They kept the deck clean after the first rain at anchor and then plugged off deck drains except for one that went to a filter and processing system. They captured all water that landed on their deck. A moderate rain filled their tanks.
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